Such valves are already known. For example, document DE 10 2005 022 693 A1 relates to a valve, in particular a proportional pressure limitation valve, having an electrically actuatable magnet system for the actuation of an actuation part, which cooperates with a valve element. The valve element is guided in a longitudinally displaceable in a valve housing and, in one of its opening positions, releases a fluid-conducting connection path between a fluid inlet and a fluid outlet. In its shut position, the valve piston shuts off this path. An energy store, preferably in the form of a compression spring, is arranged between the actuation part and the valve element at a clearance therefrom. The energy store seeks to hold the valve element in the direction of its closed position. The actuation part is designed as a guide piston, which has a longitudinal guide for the valve element. The known solution ensures that the valve element with its closure part, which, preferably having a seat design, cooperates with a valve seat in the valve housing, always arrives at its envisaged closed position in an axis-precise manner. Any angular displacement with leakage in the region of the valve seat is then reliably prevented. The known valve in principle functions in a force-controlled manner. Any undesirable dynamic effects occurring during operation of the valve are compensated for by the energy store in the form of the compensation spring.
Another valve in the form of a typical proportional pressure regulating valve is disclosed by document DE 10 2013 014 558 A1. In this known valve solution, the respective differential pressure, which is generated during passage through the additional fluid-conducting connection between the utility connection and the tank connection, acts by an actuating device on the valve piston. The valve piston, counteracting a stop position, from which position the additional fluid-conducting connection is increasingly inhibited, then passes into a fully opened open position in which, relative to the stop position, an enlarged opening cross section from the utility connection to the tank connection is achieved. An opportunity is then created to increase the valve piston stroke without having to tolerate the start-up jump of the P-I characteristic curve. The known valve can then generate a very large opening cross section when releasing a clutch connected to the valve, and nevertheless can ensure a rapid disengagement of the clutch. In this way, the clutch of a vehicle, for example, can be smoothly released, which represents a significant safety aspect, in particular in the case of mobile work machines.
Such proportional pressure regulating valves can be designed such that they generate the maximum regulation pressure without energizing of the actuating magnet system. In technical terms, this generation is expressed as these valves having a failsafe characteristic curve. With increasing current at the actuating magnet, the regulation pressure drops in a continuous manner. They are therefore frequently used for applications in which, in the case of a power outage, a safe state is obtained only when the maximum regulation pressure is applied at the consumer. It is then possible, for example, to actuate clutches that are pressurized in a de-energized manner. As a general rule however, such valves are very frequently equipped with a pilot control.